Poly(aryl ether sulfones) have been known for about two decades. They are tough linear polymers that possess a number of attactive features such as excellent high temperature resistance, good electrical properties, and very good hydrolytic stability. At least three poly(aryl ether sulfones) are commerically available. A poly(aryl ether sulfone) is available from Imperial Chemical Industries, Ltd. It has the formula (1) ##STR1## and is produced by the polycondensation of 4,4'-dihydroxydiphenyl sulfone with 4,4'-dichlorodiphenyl sulfone as described in, for example, Canadian Patent No. 847,963. The polymer contains no aliphatic moieties and has a Tg of approximately 220.degree. C.
Another commerical poly(aryl ether sulfone) is available from Amoco Performance Products, Inc., under the trademark of UDEL.RTM.. It corresponds to formula (2), ##STR2## has a Tg of about 190.degree. C., and is made via the nucleophilic polycondensation of bisphenol-A di-sodium salt with 4,4'-dichlorodiphenyl sulfone, as described in U.S. Pat. No. 4,108,837.
A third commercial poly(aryl ether sulfone) is also available from Amoco Performance Products, Inc., under the trademark of Radel.RTM. R. It corresponds to formula (3) has a Tg of about 220.degree. C., and is produced by the polycondensation of biphenol with 4,4'-dichlorodiphenyl sulfone as described in, for example, Canadian Patent No. 847,963. ##STR3##
Over the years, there has developed a substantial body of patent and other literature directed to the formation and properties of poly(aryl ether sulfones and other poly(aryl ethers) (all hereinafter called "PAE"). A broad range of PAE's was achieved by Johnson et al., J. of Polymer Science, A-1, Vol. 5, 1967, pp. 2415-2427; Johnson et al., U.S. Pat. Nos. 4,108,837 and 4,175,175. Johnson et al. show that a very broad range of PAE's can be formed by the nucleophilic aromatic substitution (condensation) reaction of an activated aromatic dihalide and an aromatic diol. By this method, Johnson et al. created a host of new PAE's.
Because of their excellent mechanical and thermal properties, coupled with outstanding hydrolytic stability, the poly(aryl ether sulfones) have been utilized in the medical market for a variety of purposes for at least ten years. These medical devices constitute a wide variety of articles. Obviously, one of the major attributes of the poly(aryl ether sulfones) is their ability to be steam autoclaved repeatedly without loss of properties. Steam autoclaving is a very severe test, requiring both high temperature and hydrolytic stability, and involving cyclical effects-wet/dry, hot/cold.
The poly(aryl ether sulfones) (1) and (2) show some important deficiencies, however. Indeed, parts molded from these materials, stress-crack when steam sterilized under stresses of say 500 psi or greater when excessive concentration of boiler additives, such as morpholine are employed to reduce corrosion in the steam generating system; or, when in contact with commonly used hospital cleaners and detergents.
While poly(biphenyl ether sulfone) (3) and parts molded therefrom have substantially better properties than poly(aryl ether sulfones (1) and (2) it is substantially more expensive than (1) and (2) due to the high cost of biphenol.
British Patent Application No. 2,088,396 describes copolymers containing units (4) and (5): ##STR4##
The claimed copolymers comprise about 80 to 10 mole percent of repeat units (4), and correspondingly about 20 to 90 mole percent of repeat units (5). The application states that the incorporation of (5) into the poly(aryl ether sulfone) (1) yields materials with improved resistance to hot water crazing. The application does not mention steam-sterilizability under load; nor does it teach that the copolymers show resistance to stress-cracking in the presence of boiler additives such as morpholine.